The present invention relates to the measurement of time delays, and more particularly to measuring delay variation of regenerated data clocks and of associated data packets.
Knowledge of the variations in the time required to transport packets having data generated at a nominally constant clock frequency allows a user to determine certain Quality of Service (QOS) parameters, and allows a service provider to manage the network so as to provide the required QOS by allocating resources more efficiently. Measurement of the transport delay of data packets and the variation of such delay is normally done either on a round-robin out-of-service basis, or is done using embedded time stamps and some sort of common clock that is available to both the source and destination. Both methods have drawbacks.
The first method cannot accomplish a unidirectional measurement and cannot exclude the possibility that compensatory delay variations may occur on the return path. The second method requires addition and subsequent deletion of the time stamps in a manner that does not compromise the payload integrity, as well as the problem in making the clock available at both the source and destination.
What is desired is a method for measuring delay variations of a regenerated data clock and of the associated data packets that is unidirectional and does not require a clock available at both the source and destination.
Accordingly the present invention provides a method of measuring delay variation of a regenerated data clock and of the associated data packets by regenerating the data clock from a reference clock at a receiver, comparing an input clock associated with the data packets with a clock derived from the regenerated clock to obtain a buffer occupancy for the data from the data packets, and obtaining a period control parameter, knob, that is representative of the delay variation in the regenerated data clock. Using the buffer occupancy and the regenerated data clock, cell arrival variations are determined from which the delay variations are inferred.
The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawing.